11 



arenaceous masses, and no lines of bedding can be found show- 

 ing planes of deposition. These arenaceous masses may or 

 may not contain erratics within their limits, as they vary 

 in this particular. The mudstones show a characteristic 

 weathering, splitting up into large slabs with a flakey ex- 

 foliation of the mass. At first these divisional lines might 

 be mistaken tor bedding planes ; but they are evidently pro- 

 duced by a rough form of cleavage, and are at a high angle. 

 This manner ot weathering tends to produce sharp serrated 

 edges along their lines of outcrop. 



The true "tilf beds are in places intercalated with laminated 

 shales, grits, and thin dolomitic limestones, which do not 

 contain erratics, and are regularly bedded. It is by these 

 regularly stratified beds intercalated with the "till" beds that- 

 the true dip of the series can be obtained. 



My first sight of this remarkable formation was sufficient 

 to convince me that I stood face to face with a true glacial 

 deposit, but repeated searching in the Valley of the Sturt 

 failed to produce any indisputable evidence of glacial wear 

 on the faces of the included boulders."*^ The shape of many 

 of these boulders was often suggestive of ice action, but con- 

 firmation was needed to place the question beyond doubt. 

 Such negative results may, perhaps, be explained from the 

 fact that the included igneous rocks are generally much de- 

 composed ; whilst others, less liable to atmospheric influences, 

 as quartz and quartzites, are frequently covered with a shaly 

 skin, left by the matrix, which effectually hides the striation 

 of the surface if existing on the stone. 



I ascertained from several sources that ''boulder beds'' were 

 seen in outcrop to the north or Adelaide, and, in search of 

 fuller proofs of glacial action (if such were obtainable), I paid 

 a visit, at the close of last year, to the neighborhoods of 

 Jamestown, Petersburg, and Oodla Wirra, nearly 200 miles 

 north of Adelaide, and obtained very definite confirmatory evi- 

 dence. The glacial beds in '^hese northern districts appear 

 to have a very wide, if intermittent, spread. 



At the Mount Grainger mine, seven miles north from 

 Oodla Wirra, two rather thin "till" beds occur, intercalated 

 Tvitli regularly bedded formations. At Petersburg, about 23 

 miles to the south-west of Oodla Wirra, there is a very ex 

 tensive development of the glacial beds. The line of strike 

 takes these beds close to the township, and can be seen in 

 a wide belt of outcrop extending for many miles in the direc- 

 tion of the strike. To the northward of the town they form 



* Since this was written good examples of glaciated boulder hove been 

 obtained. 



